ACCESSORY MAMMALIAN REPRODUCTIVE GLANDS 



383 



tose without rupture of the carbon chain; 

 (2) TPNH and DPN are required for this 

 transformation, during which sorbitol is pro- 

 duced, and becomes radioactive; (3) inhibi- 

 tors of aldose reductase {e.g., glucosonej in- 

 hibit the conversion of glucose to fructose 

 and sorbitol; and (4j sorbitol is present, 

 alongside fructose, in the secretions of sheep 

 seminal vesicle and of certain accessory 

 glands of other species [vide injra) . 



The relative importance of these phos- 

 phorylative and nonphosphorylative path- 

 ways for the biosynthesis of seminal fructose 

 remains to be determined.^ 



The fructose content of semen and of the 

 accessory glands is strictly controlled by 

 testicular hormones. The experiments of 

 Mann and Parsons (1950), depicted in Fig- 

 ure 6.7, show that in the sexually mature 

 rabbit, seminal fructose levels fell dramat- 

 ically soon after castration. This decrease 

 in seminal fructose was prevented by im- 

 plantation of a pellet of testosterone. Later 

 administration of androgen to the orchidec- 

 tomized animals restored seminal fructose 

 to normal levels. Measurement of the fruc- 

 tose content of ejaculated semen may be 

 a sensitive index of androgenic activity, 

 and has the signal advantage that the time- 

 sequence of changes which result from alter- 

 ations in the level of circulating androgen 

 can be determined without sacrifice of the 

 animal. This "fructose test" has been used 

 to assess the production of testicular andro- 

 gen, or the hormonal activity of exogenous 

 substances, in man (Harvey, 1948; Landau 

 and Longhead, 1951; Tyler, 1955; Nowa- 

 kowski and Schirren, 1956; Nowakowski, 

 1957) and in other animals (Gassner, Hill 

 and Svdzberger, 1952; Branton, D'Arens- 

 bourg and Johnston, 1952; ]\Iann and Wal- 

 ton, 1953; Glover, 1956; Davies, Mann and 

 Rowson, 1957) . 



The amounts of fructose in semen and in 

 the accessory glands are not determined 

 solely by androgenic hormones, as Mann 

 (1954a, 1956) has emphasized. The relative 

 size and storage capacity of the accessory 



^Samuels, Harding and Mann (1960) measured 

 the aldose and ketose reductase levels in the vari- 

 ous accessory glands of the rat, and in the seminal 

 vesicles of the sheep, bull, boar, and horse. They 

 found that the level of fructose production could 

 be correlated with the activity of the least of the 

 two enzymes. 



g 200 



WEEKS AFTER CASTRATION 



Fig. 6.7. Postcastrate fall and testosterone-in- 

 duced rise of seminal fructose in the rabbit. The 

 pellet contained 100 mg. of testosterone. (Redrawn 

 from T. Mann, The Biochemistry of Semen, 

 Methuen & Co., 1954.) 



glands play an important role. Another fac- 

 tor which complicates the fructose test is 

 frequency of ejaculation. In man and the 

 stallion, a single ejaculation largely depletes 

 the seminal vesicles (Mann, 1956). In the 

 bull, however, the seminal vesicles have a 

 remarkable storage capacity such that the 

 fructose content of eight consecutive ejacu- 

 lations obtained within one hour is prac- 

 tically the same (Mann, 1954a) . Blood sugar 

 levels can influence seminal fructose, but 

 there is no evidence that the abnormally 

 large quantities of fructose in diabetic semen 

 (Alann and Parsons, 1950) result from in- 

 creased output of androgenic hormones. In- 

 terruption of the blood supply to an acces- 

 sory gland is another factor which affects the 

 amount of fructose it secretes (Clegg, 1953). 

 In immature animals, there seems to be a 

 short time after birth when the accessory 

 glands will not produce fructose in response 

 to testosterone (Ortiz, Price, Williams-Ash- 

 man and Banks. 1956). Obstruction of the 

 ejaculatory ducts will, of course, prevent the 

 appearance of fructose in semen, as Young 

 (1949) found in a patient with congenital bi- 

 lateral aplasia of the vas deferens. 



